by Bradley Secker and Louise Osborne, Special for USA TODAY

by Bradley Secker and Louise Osborne, Special for USA TODAY

ANTAKYA, Turkey - Syrian activists have lashed out at signs the U.S. remains reluctant to intervene in the country's civil war despite growing evidence President Bashar al-Assad's forces have used chemical weapons against his people.

"I hope there will be a reaction from America, but I don't think there will be," said Bassam al Ahmed, 31, a Kurdish human rights activist from Qamishli in Syria. "(But) if the U.N. and the U.S. don't take any action of any kind, the Syrian regime will only have more time, and it would be a green light for the regime to use chemical weapons in the future."

The Obama administration said Thursday it could say with "varying degrees of confidence" that chemical weapons, including sarin gas, had been used at least twice by Syrian government forces on separate occasions in suburban Damascus and Aleppo.

In the Syrian capital however, a government official said Assad's military "did not and will not use chemical weapons even if it had them." He instead accused opposition forces of using them in a March attack on the village of Khan al-Assad outside of the northern city of Aleppo.

The official spoke to the Associated Press on condition of anonymity because he was not authorized to give official statements.

Syrian rebel groups including the Syrian Network for Human Rights - which told USA TODAY on Thursday they had amassed evidence including videos, photos and eyewitness testimony that showed the weapons had been used in 10 separate locations in the war-torn country - called for a Western military-enforced no-fly zone and heavier artillery, such as rocket launchers.

But even though President Obama had said the regime's use of chemical weapons would be the "red line" for the U.S., White House officials said the revelation would not lead to immediate intervention. Instead they called for further U.N. investigation to "credibly evaluate the evidence and establish what took place".

"Clearly there appears to be circumstantial evidence that that has taken place," said David Hartwell, a Middle East analyst at IHS Jane, defense and security analysts in London. "The alleged low-level usage sarin leaves open the possibility that it may not have occurred in terms of Syrian government complicity - it could be a rogue unit."

"From that point of view, I think the administration has plenty of latitude to say, hold on a second, we didn't mean that would immediately trigger intervention," he added.

Meanwhile, British Prime Minister David Cameron said in an interview with the BBC that he supported Obama on the principle of the use of chemical weapons as a "red line" and added they were looking for ways to "put pressure on the regime so we can bring it to an end."

"We need to go on gathering this evidence and also to send a very clear warning to the Syrian regime about these appalling actions," he said.

Activists reacted with anger.

"If you take the examples of Iraq and Syria, you can conclude only one thing: unless there is a strong financial incentive, the international community doesn't intervene anywhere," said U.K.-based Syrian activist Abdulwahab Omar.

"In Iraq they acted because of a suspicion there were weapons of mass destruction, but there was a financial incentive. In Syria, there is a piling amount of evidence of crimes against humanity, but no financial incentive," he said.

While western governments attempt to gather more evidence, activists said they hoped the U.S. would act soon.

"The USA never thought the Syrian government would use chemical weapons, and the red line was to buy them time not to react; it was just an excuse," said Nour Hameedo, 25, from the Idlib province in Syria, talking from Antakya.

"I don't think that anyone will react in the international community, if they wanted to, they would have done something earlier," he said.